Gaseous Mercury Detection Systems, Calibration Systems, and Related Methods

ABSTRACT

Embodiments disclosed herein are directed to gaseous mercury detection systems, calibration systems, and related methods. The gaseous mercury detection systems are configured to detect gas-phase mercury-compounds present in ambient air. For example, the gaseous mercury detection systems collect gas-phase mercury-compounds from ambient air and release the gas-phase mercury-compounds at concentrations capable of being measured by a gas-chromatography mass spectrometer without heating the gas-phase mercury-compounds above a decomposition temperature of at least one gaseous mercury compound that may present in the mercury-containing gas. The calibration systems are configured to determine an accuracy of or calibrate a gaseous mercury detection system. The disclosed calibration systems may be integrated with or distinct from the gaseous mercury detection systems disclosed herein.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.62/030,517 filed on 29 Jul. 2014, the disclosure of which isincorporated herein, in its entirety, by this reference.

GOVERNMENT SPONSORED RESEARCH

This invention was made with government support under governmentcontract no. 1324781 awarded by the National Science Foundation. Thegovernment has certain rights in the invention.

BACKGROUND

Ambient air may contain Mercury (Hg), including gas-phasemercury-compounds. Gas-phase mercury compounds may include gaseouselemental mercury (GEM) or a gaseous mercury compound(s) (GMC), such asMercury Bromide (HgBr₂), Mercury Chloride (HgCl₂), Mercury Oxide (HgO),Mercury Sulfate (HgSO₄), Mercury Nitrite (Hg(NO₂)₂), Mercury Nitrate(Hg(NO₃)₂), Mercury Iodide (HgI₂), or Mercury Fluoride (HgF₂). Other GMCtypes may also be present in ambient air.

About 1 m³ to about 10 m³ of ambient air may contain up to a few hundredpicograms (10⁻¹² grams) of GEM or GMC. At these low concentrations,typical gaseous mercury detection systems, including gaseous mercurydetection systems that include gas-chromatography mass spectrometers(GCMS), can be ineffective in accurately measuring GEM or GMC that maybe present in ambient air.

Additionally, typical gaseous mercury detection systems do not measureGMC without decomposing through high-temperature treatment the GMC,i.e., the actual compounds, into their constituent components.Conventional GEM detection systems capture GEM or GMC from ambient airinto a mercury collector and then release a high temperatures GEM or theelemental constituents of decomposed GMC into a detection device such asa cold vapor atomic fluorescence spectrometer. A conventional mercurydetection system, however, does not measure a GMC as a compound, but asits constituent elements.

FIG. 1 is a schematic diagram of a prior-art GEM detection system 100.The GEM detection system 100 includes a mercury collector 102 (e.g.,denuder) fluidly coupled to a mercury detector 104. Typically, ambientair flows through the mercury collector 102. The mercury collector 102includes a collection surface 103 configured to capture GMC from theambient air. The collection surface 103 may include a potassium chloride(KCl) coating. After collecting GMC, the mercury collector 104 and, inparticular, the collection surface 103 is heated, using a heater 106, toa high temperature in an attempt to completely release or desorb all theGMC from the collection surface 103. Such a temperature may be in excessof about 500° C.

At those high temperature, e.g., temperatures around or above 500° C.,most GMC will decompose into GEM and their elemental constituents. Forexample, a published decomposition temperature for Mercury Sulfate(HgSO₄) is 500° C. See Kurt H. Stern, High Temperature Properties andThermal Decomposition of Inorganic Salts with Oxyanions, 21 Sep. 2000, p66. Similarly, Mercury Nitrite (Hg(NO₂)₂) begins to decompose at atemperature as low as 50° C. and readily decomposes at 90° C. intoMercury Oxide (HgO) and Dinitrogen Trioxide (N₂O₃). See Id at 146.Mercury Nitrate (Hg(NO₃)₂) decomposes into Mercury Oxide (HgO)appreciably at 160° C. See Id at 147. Mercury Oxide (HgO) decomposesinto GEM at under 400° C. G. See Van Praagh, Physical Chemistry, 1950,pp 267-268. Most GMC decomposes over a range of temperatures, butgenerally speaking, the higher the temperature, the faster thedecomposition rate.

After heating the collection surface 103, the GEM or the elementalconstituents of decomposed GMC released from the collection surface 103then pass into the detector 104 to be measured. However, because thecollection surface has been heated to temperatures in excess of thedecomposition temperature of most GMC, the GMC will have decomposed intotheir elemental constituents, making the detector 104 unable toaccurately detect concentrations of the GMC as compounds initiallycollected by the collection surface 103.

Accordingly, users and designers of gaseous mercury detection systemscontinue to seek improved detection systems.

SUMMARY

Embodiments disclosed herein are directed to gaseous mercury detectionsystems, calibration systems for use with any gaseous mercury detectionsystem, and related methods. As will be discussed in more detail below,the gaseous mercury detection systems disclosed herein are configured todetect mercury-containing gases (e.g. gaseous elemental mercury (GEM) orgaseous mercury compounds (GMC or GMC) present in ambient air. Forexample, the gaseous mercury detection systems may collect GEM or GMCfrom ambient air and release the GEM or GMC at concentrations capable ofbeing measured by a gas-chromatography mass spectrometers (GCMS) withoutheating the GMC above a decomposition temperature of at least one GMCthat may have been collected. In another embodiment, the calibrationsystems disclosed herein are configured to determine an accuracy of andcalibrate a gaseous mercury detection system including any of thegaseous mercury detection systems disclosed herein. The disclosedcalibration systems may be integrated with or distinct from the gaseousmercury detection systems disclosed herein.

A gaseous mercury detection system is disclosed. The gaseous mercurydetection system includes a mercury collection surface that isconfigured to cool the mercury collection surface to a temperature ofabout 5° C. above an ambient water dew point temperature and collect onthe mercury collection surface at least one of gaseous elemental mercury(GEM) or a gaseous mercury compound (GMC) from a mercury-containing gas.The gaseous mercury detection system further includes a heaterpositioned and configured to heat the mercury collection surface to afirst release temperature and release thereby the at least one of GEM orGMC collected. The first release temperature is below a decompositiontemperature of the at least one GMC. The system further includes asample trap fluidly coupled to the mercury collector. The sample trap isconfigured to capture the at least one of GEM or GMC released from themercury collector at a temperature of about 0° C. or less and releasethe at least one of GEM or GMC captured in the sample trap at a secondrelease temperature. The second release temperature is below thedecomposition temperature of the at least one GMC. The system alsoincludes a gas-chromatography mass spectrometer fluidly coupled to thesample trap to receive the at least one of GEM or GMC released from thesample trap. In embodiments, the first release temperature is betweenabout 100° C. to about 300° C.

A gaseous mercury detection system may further include a calibrationsystem. A calibration system includes a permeation oven configured to beheated to a selected temperature and fluidly coupled to thegas-chromatography mass spectrometer. The calibration system alsoincludes one or more permeation tubes positioned within the permeationoven. Each of the one or more permeation tubes includes at least one ofelemental mercury or a mercury compound and is configured to release theat least one of the elemental mercury or the mercury compound storedtherein at the selected temperature as GEM or GMC.

In another embodiment, the permeation oven is fluidly coupled to thegas-chromatography mass spectrometer through the sample trap. A gaseousmercury detection system may further include a GEM detector fluidlycoupled to the permeation oven and configured to detect the GEM. A valvemay be fluidly coupled to the permeation oven. The valve may beconfigured to selectively control flow of the at least one of GEM or GMCreleased by the one or more permeation tubes to the gas-chromatographymass spectrometer or the GEM detector. Additionally, a pyrolyzer may bedisposed between the GEM detector and the valve. The pyrolyzer may beconfigured to heat the at least one GMC to form GEM.

In embodiments, the gaseous mercury detection system may further includeone or more conduits that fluidly couple the permeation oven with thegas-chromatography mass spectrometer. The one or more conduits may beheated to a temperature of about 100° C. to about 300° C. duringoperation.

A method of collecting and releasing gaseous elemental mercury (GEM) ora gaseous mercury compound (GMC) in ambient air is also disclosed. Themethod includes cooling a collection surface to a collection temperatureof about an ambient water dew point temperature and drawing over thecollection surface the ambient air at a collection flow rate. The methodfurther includes collecting on the collection surface substantially allof the at least one of GEM or GMC present in the ambient air and heatingthe collection surface to a temperature sufficient to release the atleast one of GEM or GMC therefrom and below a decomposition temperatureof the at least one GMC. The method also includes releasing from thecollection surface substantially all of the at least one of GEM or GMCcollected thereon.

A method of measuring a quantity of GEM or GMC in ambient air is alsodisclosed. The measuring method includes collecting and releasing GEM orGMC in ambient air, as described above. The measuring method alsoincludes cooling a sample trap to a temperature of about 0° C. or lessand capturing the at least one of the GEM or GMC released from themercury collector with a sample trap. The measuring method also includesheating the sample trap to a temperature greater than about 100° C. andbelow the decomposition temperature of the at least one GMC, desorbingthe at least one of GEM or GMC from the sample trap. Finally, afterheating the sample trap, the measurement method includes measuring atleast one of a quantity of the GEM or GMC using a gas-chromatographymass spectrometer.

In embodiments, heating the collection surface in the measurement methodincludes heating the collection surface to a temperature of about 100°C. to about 300° C. In another embodiment, cooling the collectionsurface to a collection temperature includes cooling the collectionsurface to a collection temperature of five degrees above the ambientwater dew point temperature. Similarly, in an embodiment, the collectionflow rate may be between about 10 to about 100 liters per minute andcollecting on the collection surface may occur over a period of 30minutes to two hours. In another embodiment, cooling the sample trapincludes cooling the sample trap to a temperature of about −50° C.

In another embodiment, the measurement method may include, prior tomeasuring, ionizing the at least one mercury-containing gas using anelectron ionizer or a chemical ionizer.

The measurement method may further include calibrating thegas-chromatography mass spectrometer. The calibration method includesheating a permeation oven to a selected temperature, the permeation ovenincluding one or more permeation tubes therein having at least one ofelemental mercury or a mercury compound and configured to release the atleast one of the elemental mercury or the mercury compound storedtherein at the selected temperature as GEM or GMC. The calibrationmethod further includes measuring the quantity of the at least one ofthe GEM or the GMC released by the one or more permeation tubes usingthe gas-chromatography mass spectrometer.

A calibration system is also disclosed. The calibration system includesa permeation oven configured to be heated to a selected temperature andone or more permeation tubes positioned within the permeation oven. Eachof the one or more permeation tubes includes elemental mercury or amercury compound and is configured to release the elemental mercury orthe mercury compound stored therein at the selected temperature as GEMor GMC. The calibration system further includes a GEM detectorconfigured to detect the GEM and one or more conduits coated with asubstantially nonpolar coating and configured to fluidly couple thepermeation oven to the GEM detector, the one or more conduits furtherconfigured to be heated to a temperature above about 120° C. duringoperation. In embodiments, the calibration system may further include apyrolyzer configured to heat the at least one of GEM or at least one GMCto a temperature above the decomposition temperature of the GMC.

Features from any of the disclosed embodiments may be used incombination with one another, without limitation. In addition, otherfeatures and advantages of the present disclosure will become apparentto those of ordinary skill in the art through consideration of thefollowing detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of embodiments of the present disclosure willbecome more fully apparent from the following description and appendedclaims, taken in conjunction with the accompanying drawings.Understanding that these drawings depict only typical embodiments of thepresent disclosure and are, therefore, not to be considered limiting ofits scope, the embodiments of the present disclosure will be describedwith additional specificity and detail through use of the accompanyingdrawings in which:

FIG. 1 is a schematic diagram of a prior-art GEM detection system;

FIGS. 2A and 2B are schematic diagrams of different portions of agaseous mercury detection system, according to an embodiment;

FIG. 3 is a flow diagram of a method of using the gaseous mercurydetection system shown in FIGS. 2A and 2B, according to an embodiment;

FIG. 4 is a schematic diagram of a gaseous mercury detection systemconfigured to accurately measure GEM or GMC in ambient air and includingat least part of an integrated calibration system, according to anembodiment;

FIG. 5 is a flow diagram of a method of using the gaseous mercurydetection system shown in FIG. 4, according to an embodiment;

FIGS. 6A and 6B are graphs outputted by a GCMS after the GCMS measured aquantity of different mercury-containing gases; and

FIG. 7 is a schematic illustration of a calibration system that may beused to calibrate any gaseous mercury detection system disclosed hereinor conventional gaseous mercury detection systems, according to anembodiment.

DETAILED DESCRIPTION

Embodiments disclosed herein are directed to gaseous mercury detectionsystems, calibration systems for use with any gaseous mercury detectionsystem, and related methods. As will be discussed in more detail below,the gaseous mercury detection systems disclosed herein are configured todetect gas-phase elemental mercury or gaseous mercury compounds (e.g.GEM or GMC) present in ambient air. For example, the gaseous mercurydetection systems collect the low concentrations of GMC from ambient airand then release the GMC at a concentration capable of being measured bya GCMS without heating the GMC above a decomposition temperature of atleast one GMC collected. The calibration systems disclosed herein areconfigured to determine the accuracy of and calibrate the gaseousmercury detection systems. The disclosed calibration systems may beintegral with or distinct from the gaseous mercury detection systems.

In the following description, numerous specific details are provided fora thorough understanding of specific embodiments. However, those skilledin the art will recognize that embodiments can be practiced without oneor more of the specific details, or with other methods, components,materials, etc. In some cases, well-known structures, materials, oroperations are not shown or described in detail in order to avoidobscuring aspects of the preferred embodiments. Furthermore, thedescribed features, structures, or characteristics may be combined inany suitable manner in a variety of additional embodiments. Thus, thefollowing more detailed description of the embodiments, as illustratedin some aspects in the drawings, is not intended to limit the scope ofthe present disclosure, but is merely representative of the variousembodiments of the present disclosure.

In this specification and the claims that follow, singular forms such as“a,” “an,” and “the” include plural forms unless the content clearlydictates otherwise. All ranges disclosed herein include, unlessspecifically indicated, all endpoints and intermediate values. Inaddition, “optional”, “optionally”, or “or” refer, for example, toinstances in which subsequently described circumstance may or may notoccur, and include instances in which the circumstance occurs andinstances in which the circumstance does not occur. The terms “one ormore” and “at least one of . . . or . . . ” refer, for example, toinstances in which one of the subsequently described circumstancesoccurs, and to instances in which more than one of the subsequentlydescribed circumstances occurs.

FIGS. 2A and 2B are schematic diagrams of different portions of agaseous mercury detection system 200, according to an embodiment. Thegaseous mercury detection system 200 may include a mercury collector 202(e.g., a denuder) pneumatically coupled to a pump 208 (FIG. 2A). Thepump 208 may be configured to draw and flow ambient air through themercury collector 202. The mercury collector 202 includes a collectionsurface 203 configured to collect GMC from the ambient air flowingthrough the mercury collector 202. The mercury collector 202 is furtherconfigured to release GMC from the mercury collector 202 when heated toa first release temperature that is below a decomposition temperature ofthe at least one GMC that may have been collected on the mercurycollector 202. The mercury collector 202 is further fluidly coupled to asample trap 210 (e.g., a cryogenically cooled sample trap). The sampletrap 210 includes a trapping surface 231 configured to be cooled to atemperature that captures the GEM or GMC thereon. The sample trap 210and, in particular, the trapping surface 231, may be configured torelease the GEM or GMC by heating the sample trap 210 and the trappingsurface 231 thereof to a second release temperature that is below thedecomposition temperature of the at least one GMC. In some embodiments,the sample trap 210 may be fluidly coupled to a GCMS 204. The sampletrap 210 may be configured to release the GEM or GMC therefrom at aconcentration that can be measured by the GCMS 204. The GCMS 204 mayinclude a column 212 and a mass spectrometer 214. The GCMS 204 may beconfigured to detect at least one of GEM or GMC present in the at leastone mercury-containing gas. In particular, the GCMS 204 may detect GMCbecause the gaseous mercury detection system 200 is not heated to atemperature above the decomposition temperature of the GMC. The gaseousmercury detection system 200 may further include a controller 246 thatcontrols one or more components of the gaseous mercury detection system200.

Referring to FIG. 2B, the gaseous mercury detection system 200 may behoused in a support structure 215. The mercury collector 202 may includea first wall 216 that partially defines an internal collection chamber218. The first wall 216 may also include a first inlet 220 and a firstoutlet 222 spaced from the first outlet 222. The first inlet 220 and thefirst outlet 222 are in fluid communication such that ambient air canflow therebetween and through the collection chamber 218.

As discussed above, the mercury collector 202 includes the collectionsurface 203 that is at least partially positioned within or defines thecollection chamber 218. The collection surface 203 may be positioned tobe exposed to ambient air that flows through the collection chamber 218.In an embodiment, the collection surface 203 may be defined by a coatingthat coats at least a portion of the first wall 216. In an embodiment,the collection surface 203 may include a feature that is at leastpartially positioned within the collection chamber 218. For example, thefeature may include a plurality of fibers, a plurality of beads, agrate-like structure extending from the wall 216, a generally foam-likestructure, another suitable feature, or combinations thereof. At least aportion of the surface of the feature may form at least a portion of thecollection surface 203. As such, the feature may increase a surface areaof the collection surface 203 that is exposed to the ambient air flowingthrough the collection chamber 218. In some embodiments, increasing thesurface area of the collection surface 203 may increase the quantity ofGEM or GMC that is collected by the collection surface 203.

The collection surface 203 may include any surface or materialconfigured to collect GEM or GMC from the ambient air flowing throughthe mercury collector 202. A GMC may be Mercury Bromide (HgBr₂ or HgBr),Mercury Chloride (HgCl₂), Mercury Oxide (HgO), Mercury Sulfate (HgSO₄),Mercury Nitrite (Hg(NO₂)₂), Mercury Nitrate (Hg(NO₃)₂), Mercury Iodide(HgI₂), Mercury Fluoride (HgF₂), or another GMC.

Additionally, in some embodiments, the collection surface 203 may beconfigured to collect and release GEM or GMC at one or more selectedtemperatures. For example, the collection surface 203 may include anysurface or material that may collect GEM or GMC at ambient temperaturesor below. For example, the mercury collector 202 may be configured tocool the collection surface 203 to a few degrees above an ambient waterdew point temperature, e.g., five degrees above the ambient dew pointtemperature. Maintaining the collection surface 203 slightly above theambient dew point temperature during the collection process allows themercury collector 202 to capture GEM or GMC without also capturingsignificant amounts of water vapor in the ambient air. Condensed watervapor on the collection surface 203 could chemically interact with theGEM or GMC such that downstream measurements of GEM or GMC would beinaccurate.

Having a collection surface 203 that is maintained at or a few degreesabove an ambient water dew point temperature may also negate the need topre-condition or dry the ambient air prior to collecting GEM or GMC onthe collection surface 203. Pre-conditioning, including filtering, orremoving water vapor by cooling and then heating the ambient air, maycause some GMC to decompose on the conditioning surfaces. Thus,pre-conditioning the ambient air may lead to inaccurate quantificationof GMC present in the ambient air.

Additionally, the collection surface 203 may include any surface ormaterial configured to release the captured GEM or GMC at a firstrelease temperature. The first release temperature or desorptiontemperature may be any temperature that is greater than the temperatureat which the collection surface 203 collects the GEM or GMC and below adecomposition temperature of at least one (e.g., some or all) GMCcollected by the collection surface 203. The release or desorptiontemperature for a given GMC is assumed to be below the range ofdecomposition temperatures of the same GMC. The decompositiontemperature is a temperature at which the GMC begins to decompose intoGEM and its elemental constituents. The published decompositiontemperatures for various GMC is described in the background section. Atleast one GMC may partially decompose below the first releasetemperature due to factors unrelated to heat, such as barometricpressure, time, the presence of other chemical compounds, or theinteraction of the GMC with the collection surface 203.

The time required to desorb GMS from the collection surface may varydepending on the type of collection surface, the GMC compound beingdesorbed, or other factors, but typical desorption times may be between5 and 60 minutes.

The exact decomposition temperature may vary depending on which GMC arepresent. The inventor of the present disclosure has found that a releasetemperature of between 100° C. to about 200° C. provides a gooddesorption rate while preventing significant decomposition of most ifnot all GMC. As such, the first release temperature may be about 80° C.to about 300° C., such as 100° C. to about 200° C., about 140° C. toabout 220° C., about 150° C. to about 200° C., or about 160° C. to about180° C. However, in some embodiments, and for some GMC, the firstrelease temperature may be greater than about 300° C.

The collection surface 203 may include any material that can collect GEMor a GMC at ambient temperatures or below and release the at least onemercury-containing gas at the first release temperature. In anembodiment, the collection surface 203 may include quartz (e.g.,deactivated fused silica), nylon, polydimethylsiloxane (PDMS), anotherinert material, or combinations thereof. For example, the collectionsurface 203 may include a coating (e.g., a deactivated fused silicacoating, a PDMS coating), a plurality of fibers (e.g., a plurality ofquartz wool fibers, a plurality of PDMS-coated fibers, or combinationsthereof), or combinations thereof.

In an embodiment, the first inlet 220 of the mercury collector 202 maybe exposed to ambient air, while the first outlet 222 of the mercurycollector 202 may be fluidly coupled to a pump 208 (FIG. 2A) via a firstconduit 224. The pump 208 may be configured to draw and flow air throughthe first inlet 220 at a selected flow rate. A flow rate may be chosento provide the correct air speed for the collection surface 203 tocapture and retain substantially all of the GEM or GMC flowing over orthrough the collection surface 203. For example, the selected flow ratemay be chosen to enable the collection surface 203 to collect GEM or GMCflowing thereover and retain the GEM or GMC previously collected by thecollection surface 203.

Analogous to an air filter capturing and retaining particulate matterfrom an air stream, a high flow rate may provide more GEM or GMC flowingover or through the collection surface 203 but less GEM or GMC may becollected and retained on the collection surface 203 due to the high airvelocities. Thus an excessively high flow rate could lead to inaccuratequantification of GEM or GMC present in the ambient air. Conversely, alow flow rate may provide for capturing substantially all of the GEM orGMC flowing over or through the collection surface 203 but aninsufficient amount of GEM or GMC may be collected that might be laterquantified by a GCMS, e.g., GCMS 204. A low flow rate may be compensatedfor by having a longer collection time. However, a longer collectiontime might also lead to an inaccurate quantification of GMC present inthe ambient air as some GMC may decompose due to their interaction withthe collection surface 203 over excessive time periods. Shortercollection times are preferred to prevent spontaneous decomposition ofcollected GMC over time. A low flow rate may also be compensated for byincreasing the exposed area of collection surface 203. The rate at whichthe pump 208 draws ambient air through the first inlet 220 may beselected based on a volume of the collection chamber 218, an area of thefirst inlet 220 or the first outlet 222, a surface area of thecollection surface 203 exposed to the ambient air, or a material fromwhich the collection surface 203 is formed.

The inventor of the present disclosure has found a good collection rateand time is from between about 10 and 100 liters per minute (0.6 m³ toabout 6 m³ per hour) over a period of 30 minutes to two hours. In otherwords, the pump 208 may draw ambient air through the first inlet 220 andover the collection surface 203 at that rate and for that duration tocollect and derive an accurate quantification of GEM or GMC present inthe ambient air. In some embodiments, e.g., with a larger collectionsurface 203, the pump 208 may be configured to draw air at a rate ofmore than 10 m³/hr. The pump 208 may draw ambient air through the firstinlet 220 in response to direction from the controller 246.

Referring to FIG. 2B, the mercury collector 202 may be thermally coupledto a first heater 206. The first heater 206 may be configured to heatthe mercury collector 202 and, in particular, the collection surface 203thereof, to a first release temperature. For example, the first heater206 may include a resistive heating coil that is wrapped around anexterior of the mercury collector 202 or one or more Peltier cellsthermally coupled to the mercury collector 202. In an embodiment, thefirst heater 206 may be at least partially positioned within, about, orincorporated into the mercury collector 202. The first heater 206 mayalso be configured to reduce the temperature of the mercury collector202 to an ambient water dew point temperature or below (e.g., the firstheater 206 may be integrated with cooling device to form a temperaturecontrol device that includes both heating and cooling elements). Inparticular, the first heater 206 may cool the mercury collector 202 fromthe first release temperature back to a few degrees within an ambientwater dew point temperature. Similarly, the first heater 206 maymaintain the mercury collector 202 at a selected temperature when themercury collector 202 is in an environment that is above typical ambienttemperatures. The first heater 206 may heat and cool (if integrated witha cooling device) the mercury collector 202 in response to directionfrom the controller 246.

A relatively low release temperature may cause the mercury collector 202to release GEM or GMC at a concentration too low to be accuratelymeasured by the GCMS 204. As such, embodiments of the gaseous mercurydetection system 200 may further include a sample trap 210 that isfluidly coupled to the mercury collector 202 via one or more secondconduits 226. The sample trap 210 may be configured to collect and thenselectively release, by heating to different temperatures correspondingto different desorption temperatures of GEM or specific GMC types, GEMor GMC at a concentration that can be accurately measured by the GCMS204.

In an embodiment, the mercury collector 202 may be fluidly coupled toboth the pump 208 (FIG. 2A) and the sample trap 210 substantiallysimultaneously. Additionally or alternatively, the mercury collector 202may be fluidly coupled to only one of the pump 208 or the sample trap210 at a given time. For example, the mercury collector 202 mayinitially be fluidly coupled to the pump 208. After ambient air hasflowed through the mercury collector 202, the mercury collector 202 maybe fluidly decoupled (e.g., physically decoupled from) from the pump 208and the mercury collector 202 may then be fluidly coupled to the sampletrap 210. In this latter configuration, the mercury collector may beoperated in the field and then returned to a laboratory environment totransfer the collected GEM or GMC to the sample trap 210.

In some embodiments, a carrier gas may be flowed from the mercurycollector 202 to the sample trap 210 to facilitate the flow of GEM orGMC from the collection surface 203 to the sample trap 210. The carriergas may include dry ambient air or, more particularly, a gas that isnon-reactive with the at least one mercury-containing gas (e.g., Argon,Helium, or another noble gas or another inert gas). A dry, inert gas mayincrease the desorption rate or reduce or prevent the decomposition ofGEM or GMC collected on the collection surface 203. A faster desorptionrate or reduced decomposition of GEM or GMC will aid in more accuratelymeasuring the quantity of GEM or GMC collected from the ambient air.

The sample trap 210 may include a second wall 228 that defines aninternal trapping chamber 230. The trapping chamber 230 may furtherinclude a second inlet 232 and a second outlet 234 formed therein. Thesecond outlet 234 may be spaced from the second inlet 232. The secondinlet 232 may be fluidly coupled to the first outlet 222 through thesecond conduit 226. The sample trap 210 may further include a trappingsurface 231 at least partially positioned within the trapping chamber230. The trapping surface 231 may be attached to, at least partiallypositioned in, or incorporated into at least a portion of the secondwall 228. In an embodiment, a portion of the trapping surface 231 mayextend from the second wall 228 into trapping chamber 230. The trappingsurface 231 may partially define the trapping chamber 230.

The trapping surface 231 may be cooled to a temperature sufficient tocapture at least some of (e.g., substantially all of) the GEM or GMCflowing between the second inlet 232 and the second outlet 234. Forexample, the trapping surface 231 may be cooled to a condensationtemperature of GEM or a GMC, typically in the range of 0° C. to as lowas −50° C. The condensation temperature may be any temperature thatcauses at least one GEM or GMC captured in the mercury collector 202 tocondense on the trapping surface 231. In an embodiment, the trappingsurface 231 may be configured to capture a mercury-containing gas whenthe trapping surface 231 exhibits a temperature below about 0° C., suchas below about −5° C., or below about −10° C.

In an embodiment, the trapping surface 231 may be cooled using a coolingdevice (not shown), including a chiller or a suitable cryogenic coolerthat is thermally coupled to the trapping surface 231. In an embodiment,the sample trap 210 may include one or more Peltier cells forcontrolling the temperature of the sample trap 210. In an embodiment,the sample trap 210 may be cooled using any suitable cooling deviceknown in the art.

In an embodiment, the sample trap 210 may further include a secondheater 236 thermally coupled to the sample trap 210 and, in particular,the trapping surface 231. The second heater 236 may include a pluralityof resistive heating coils wrapped around or incorporated into thesample trap 210, one or more Peltier cells, or any suitable heatingdevice. The second heater 236 may be configured to rapidly heat thesample trap 210 and, in particular, the trapping surface 231 to a secondrelease temperature. The second release temperature may include anytemperature above the condensation temperature (e.g., greater than about100° C.) and below a decomposition temperature of the at least one GMCthat may be present in the at least one mercury-containing gas. Forexample, the second release temperature may about 100° C. to about 300°C., such as about 120° C. to about 250° C., and about 150° C. to about200° C. In some embodiments, the second release temperature may besubstantially similar to, greater than, or less than the first releasetemperature. The second heater 236 may be configured to rapidly heat thetrapping surface 231 to the second release temperature in about 2seconds to about 2 minutes, such as about 5 seconds to about 10 seconds,less than about 1 minute, or about 10 seconds to about 30 seconds.Rapidly heating the sample trap 210 may release the GEM or GMC in aconcentration that may be accurately measured by the GCMS 204. In someembodiments, the cooling device may be integrated with the second heater236 to form a temperature control device.

In an embodiment, the gaseous mercury detection system 200 may include atemperature control unit 237 communicably coupled to the sample trap210. For example, the temperature control unit 237 may be incorporatedinto the sample trap 210, attached to the sample trap 210, may be remotefrom the sample trap 210, or may be incorporated into the controller246. The temperature control unit 237 may direct the cooling devicecoupled to the sample trap 210 to cool the trapping surface 231 to thecondensation temperature. Similarly, the temperature control unit 237may be configured to direct the second heater 236 to rapidly heat thesample trap 210 to the second release temperature. In an embodiment, thetemperature control unit 237 may be coupled to a thermometer (not shown)or other thermal sensor that determines the actual temperature of thesample trap 210. In some embodiments, the temperature control unit 237may be omitted. In some embodiments, the temperature control unit 237may be integrated with the controller 246.

In an embodiment, the temperature control unit 237 may also becommunicably coupled to the mercury collector 202. In such anembodiment, the temperature control unit 237 may direct the first heater206 to heat the mercury collector 202 to the release temperature. In anembodiment, the gaseous mercury detection system 200 may be communicablycoupled to a separate temperature control unit. Alternatively, themercury collector 202 may not be communicably coupled to a temperaturecontrol unit.

The column 212 of the GCMS may include one or more column inlets 238 andone or more column outlets 240 that are spaced from the column inlet238. The column 212 may be fluidly coupled to the sample trap 210. Forexample, the second outlet 234 of the sample trap 210 may be fluidlycoupled to the column inlet 238 via one or more third conduits 242. Insome embodiments, a carrier gas may be flowed from the sample trap 210to the GCMS 204 to help flow the at least one mercury-containing gasfrom the sample trap 210 to the column 212. The carrier gas may includeambient air or, more particularly, a gas that is non-reactive with theat least one mercury-containing gas (e.g., Argon, Helium, or other noblegas and/or other inert gas). The carrier gas may also be easilychemically distinguishable by the GCMS 204 from the at least onemercury-containing gas to be analyzed.

The column 212 may include a stationary phase (not shown) therein. Thestationary phase may be positioned within the column 212 such that amobile phase (e.g., the GEM or GMC) flows through at least a portion ofthe stationary phase. The stationary phase may include a substantiallynonpolar stationary phase. For example, the stationary phase may includedeactivated fused silica or PDMS. The substantially nonpolar stationaryphase may be less likely to have GEM or GMC strongly adhere thereto.

The mass spectrometer 214 of the GCMS 204 may be fluidly coupled to thecolumn outlet 240 of the column 212. Upon entering the mass spectrometer214, the GEM or GMC may be ionized using an ionizer 244. In anembodiment, the ionizer 244 may include an electron ionizer. Theelectron ionizer may bombard the GEM or GMC with free electrons that areemitted from a filament to ionize the GEM or GMC. The GEM or GMC may ormay not be cooled before being ionized. In an embodiment, the ionizer244 may include a chemical ionizer. The chemical ionizer may be lesslikely to fragment or decompose any GMC present into its individualelements than the electron ionizer. The chemical ionizer may introduce areagent gas, such as methane. The reagent gas then chemically interactswith the GEM or GMC to ionize the GEM or GMC. The ionizer 244 may ionizethe GEM or GMC in response to direction from the controller 246.

After the GEM or GMC is ionized, the mass spectrometer 214 may analyzethe GEM or GMC to determine a quantity of GEM or GMC present. The massspectrometer 214 used to analyze the GEM or GMC may include a massselective detector, an ion trap mass spectrometer, a magnetic sectormass spectrometer, or another suitable mass spectrometer. The massspectrometer 214 may measure the GEM or GMC in response to directionfrom the controller 246.

In some embodiments, one or more components of the gaseous mercurydetection system 200 may be heated to a temperature below thedecomposition temperature of at least one GMC present to at leastpartially prevent (e.g., substantially prevent) the GMC from stickingthereto. For example, at least one of the second conduit 226, the thirdconduit 242, the column 212, or another component of the gaseous mercurydetection system 200 may be heated to about 100° C. to about 300° C.,such as about 150° C. to about 250° C. In such a case, the gaseousmercury detection system 200 may include one or more heaters (not shown)that heats the one or more components. Additionally, the temperature ofthe one or more components of the gaseous mercury detection system 200may be controlled by the temperature control unit 237, by anothertemperature control unit, or by the controller 246. In an embodiment,one or more components of the gaseous mercury detection system 200 mayinclude a substantially nonpolar coating that coats an interior surfacethereof that contacts the GEM or GMC. The coating may at least partiallyprevent (e.g., substantially prevent) the GEM or GMC from stickingthereto. For example, at least one of the second conduit 226, the thirdconduit 242, the column 212, or another component of the gaseous mercurydetection system 200 may include deactivated fused silicamaterial/coating or PDMS coating applied to an internal surface thereof.

As previously discussed, the controller 246 may be configured to controlone or more components of the gaseous mercury detection system 200. Thecontroller 246 may include a user interface 248 configured to enable auser of the gaseous mercury detection system 200 to communicate with thecontroller 246. For example, the user interface 248 may enable a user toupload instructions into the gaseous mercury detection system 200.Additionally, the user interface 248 may enable the controller 246 tocommunicate information to the user, such as the status of an operationor the quantities of GEM or GMC detected by the GCMS 204. The controller246 may further include memory 250 configured to store instructions andprograms thereon. The controller 246 may further include one or moreprocessors 252 configured to execute the instructions and programsstored on the memory 250.

FIG. 3 is a flow diagram of a method 300 of using the gaseous mercurydetection system 200 shown in FIGS. 2A and 2B, according to anembodiment. In some embodiments, some of the acts of the method 300 maybe split into a plurality of acts, some of the acts may be combined intoa single act, and some acts may be omitted. Also, additional acts may beadded to the method 300.

In act 305, the mercury collector 202 collects GEM or GMC from ambientair. In act 310, the mercury collector 202 is heated to the firstrelease temperature using the first heater 206. The mercury collector202 may be heated after the collection surface 203 has had sufficienttime to collect the GEM or GMC from the ambient air, i.e., a sufficientamount of GEM or GMC to be accurately measured by the GCMS 204 after theGEM or GMC is or are concentrated by the sample trap 210.

In act 315, the sample trap 210 and, in particular the trapping surface231, captures GEM or GMC released from the mercury collector 202. Forexample, the trapping surface 231 of the sample trap 210 may be cooledto a condensation temperature that is less than about 0° C.

In act 320, the sample trap 210, and in particular the trapping surface231, may be rapidly heated to the second release temperature. The sampletrap 210 may be heated to the second release temperature in about 2seconds to about 2 minutes. Rapidly heating the sample trap 210 maycause the GEM or GMC to exit the sample trap 210 in higherconcentrations than when the GEM or GMC exited the mercury collector202. The higher concentrations of GEM or GMC may enable the GCMS 204 tomeasure the collected GEM or GMC.

In act 325, the GEM or GMC released from the sample trap 210 flows intothe column 212 of the GCMS 204. The stationary phase of the column 212may interact with the gases flowing therethrough to separate the GEM orGMC from other gases that flow through the column 212. Additionally, insome embodiments, the column 212 may interact with the GEM or GMC toseparate individual constituents of the GEM or GMC from each other. Forexample, the column 212 may separate the GEM or each GMC from eachother.

In act 330, the GEM or GMC that has passed through the column 212 entersthe mass spectrometer 214 and may be measured to determine the quantityof the captured GEM or GMC. In some embodiments, prior to beingmeasured, the GEM or GMC may be ionized by the ionizer 244. The ionizer244 may include an electron ionizer, a chemical ionizer, or any suitableionizer as previously described. The GCMS 204 may ionize and measure theGEM or GMC in response to direction from the controller 246.

In optional act 335, one or more components of the gaseous mercurydetection system 200 may be heated to a temperature below adecomposition temperature of at least one GMC captured from the ambientair. The temperature may be selected to prevent at least one GEM or GMCfrom sticking to a surface of gaseous mercury detection system 200. Forexample, at least one of the second conduit 226 or the third conduit 242may be heated to a temperature of about 100° C. to about 300° C.

FIG. 4 is a schematic diagram of a gaseous mercury detection system 400configured to accurately detect GEM or GMC in ambient air and includesat least part of an integrated calibration system, according to anembodiment. In particular, the gaseous mercury detection system 400 mayinclude a plurality of components configured to measure a quantity ofGEM or GMC in ambient air, and a plurality of additional components(e.g., a permeation oven) configured to determine an accuracy of orcalibrate the gaseous mercury detection system 400.

The gaseous mercury detection system 400 may include one or morecomponents that are substantially similar to the components shown inFIGS. 2A and 2B, e.g., a support structure 415 and a mercury collector402 with a collection surface 403 configured to collect GEM or GMC fromthe ambient air. The mercury collector 402 and, in particular, thecollection surface 403 may be configured to release the GEM or GMC whenthe mercury collector 402 is heated to a first release temperature. Thegaseous mercury detection system 400 may also include a sample trap 410that is configured to release GEM or GMC in a concentration that can beaccurately measured by the GCMS 404. For example, the sample trap 410includes at least one trapping surface 431 configured to capture GEM orGMC released by the mercury collector 402. The sample trap 410 may thenbe rapidly heated to a second release temperature to release the GEM orGMC therefrom. The GEM or GMC may then flow into a GCMS 404 thatmeasures the quantity of GEM or GMC present in the ambient air.

The gaseous mercury detection system 400 may include one or more valvesconfigured to fluidly couple the components of the gaseous mercurydetection system 400 to each other and controllably direct the flow ofthe GEM or GMC to the different components. For example, in theillustrated embodiment, the gaseous mercury detection system 400includes a first valve 454 and a second valve 456. The first valve 454may fluidly couple the mercury collector 402 to the second valve 456.The second valve 456 may fluidly couple the first valve 454, the sampletrap 410, and the GCMS 404 to each other. The first valve 454 and thesecond valve 456 may be also fluidly couple one or more components ofthe detection system to a vent 458. The first valve 454 and the secondvalve 456 may be any suitable valve, such as a multi-port valve, anelectrically activated valve, or combinations thereof. In someembodiment, at least one of the first valve 454 or the second valve 456may direct the flow of the at least one mercury-containing gas inresponse to direction from the controller 444, from manual operation bya user of the gaseous mercury detection system 400, or any suitablemethod. In some embodiments, additional valves (e.g., a third valve) maybe added to the gaseous mercury detection system 400. In otherembodiments, the first valve 454 and the second valve 456 may becombined into a single valve. In other embodiments, the first valve 454and the second valve 456 may be omitted.

The gaseous mercury detection system 400 further includes a permeationoven 460 that functions as part of a calibration system and isconfigured to determine an accuracy of or calibrate the gaseous mercurydetection system 400. For example, the permeation oven 460 is configuredto supply a known quantity of GEM or GMC. The known quantity of GEM orGMC may then be measured by the gaseous mercury detection system 400 tomeasure the quantity of GEM or GMC in ambient air. The known quantity ofGEM or GMC supplied by the permeation oven 460 may be compared to thequantity of GEM or GMC measured by the gaseous mercury detection system400 to determine the accuracy or calibrate the gaseous mercury detectionsystem 400.

The permeation oven 460 may include at least one oven wall 462 thatdefines an internal heating chamber 464. The oven wall 462 may define atleast one oven inlet 466 and at least one oven outlet 468 spaced fromthe oven inlet 466. The permeation oven 460 may be configured to have afluid flow from the oven inlet 466 to the oven outlet 468. Thepermeation oven 460 may further include a filament or other heatingdevice (not shown) positioned therein configured to heat the heatingchamber 464 and contents therein to a selected temperature. The selectedtemperature may be any temperature below the decomposition temperatureof at least one GMC supplied by the permeation oven 460. For example,the selected temperature may less than about 300° C., less than about200° C., or about 100° C. The filament or other heating device may beconfigured to heat the heating chamber 464 to a selected temperature inresponse to direction from the controller 446.

The permeation oven 460 may also include one or more permeation tubes470 positioned in the heating chamber 464. The permeation tubes 470 mayinclude a compartment therein including elemental mercury or a mercurycompound positioned therein. At least a portion of the permeation tubes470 that defines the compartment may include a material that issemi-permeable to a vapor or gas of GEM or GMC (e.g., a permeablemembrane), such as polyfluoroalkoxy alkane Teflon® heat shrinkingtubing. At the selected temperature, the elemental mercury or mercurycompound present in the compartment may evaporate or otherwise form GEMor a GMC. The GEM or GMC may be emitted from the permeation tubes 470.At a constant temperature, the emission rate of GEM or GMC may besubstantially constant. The emission rate of the GEM or GMC at theselected temperature may be known (e.g., previously known or calculatedby comparing the weight of the permeation tube 470 before and after thepermeation tube 470 is heated).

In an embodiment, the permeation oven 460 may be configured to have agas flow through the heating chamber 464 that is non-reactive with GEMor GMC. For example, the permeation oven 460 may be fluidly coupled to agas supply 472 via at least one fourth conduit 474. The gas supply 472may include, for example, a pressurized cylinder or a pump. The fourthconduit 474 may flow the gas from the gas supply 472 into the heatingchamber 464 via the oven inlet 466.

In an embodiment, the permeation oven 460 may include one or morecontainers 476 positioned in the heating chamber 464 configured tosupport the one or more permeation tubes 470. Each container 476 may bepositioned and configured such that a gas flowing through the heatingchamber 464 flows around one or more individual permeation tubes 470 oraround all permeation tubes 470 positioned on the containers 476.Additionally, the containers 476 may be configured to expose eachpermeation tube 470 to the selected temperature or to different, knowntemperatures, e.g., each permeation tube 470 may be heated to adifferent temperature.

In an embodiment, the containers 476 are configured to expose eachpermeation tube 470 positioned thereon to the heating chamber 464. Forexample, the container 476 may include a generally plate-like structure.In an embodiment, the containers 476 are configured to substantiallyseal the permeation tubes 470 from the heating chamber 464. For example,the containers 476 may include a generally conduit-like structure thatis coupled to the oven inlet 466 via a conduit (e.g., the fourth conduit474) and the oven outlet 468 via a conduit (e.g., the fifth conduit480).

The permeation oven 460 is configured to flow a gas around eachpermeation tube 470 at a selected flow rate. For example, the fourthconduit 474 may be fluidly coupled to one or more orifices 478. Each ofthe orifices 478 may selectively control the rate at which the gas fromthe fourth conduit 474 flows therethrough. Each of the orifices 478 mayalso be fluidly coupled to one or more containers 476 that substantiallyseal each permeation tube therein from the rest of the heating chamber464. As such, each permeation tube 470 may be exposed to a selected flowrate of the gas. The orifices 478 may operate in response to directionfrom the controller 446.

The permeation oven 460 may be fluidly coupled to one or more componentsof the gaseous mercury detection system 400. For example, in theillustrated embodiment, the permeation oven 460 may be fluidly coupledto the first valve 454 via at least one fifth conduit 480. Thepermeation oven 460 may then be fluidly coupled to at least one of thesample trap 410 or the GCMS 404 via the second valve 456. For example,the second valve 456 may direct the GEM or GMC supplied by thepermeation oven 460 directly to the GCMS 404. Alternatively, the secondvalve 456 may direct the GEM or GMC to the sample trap 410 to beconcentrated before directing the GEM or GMC to the GCMS 404. In anembodiment, the GEM or GMC supplied by the permeation oven 460 may firstbe directed to the mercury collector 402 before being directed to thesample trap 410 or the GCMS 404.

The GCMS 404 may measure the quantity of GEM or GMC supplied by thepermeation oven 460. The gaseous mercury detection system 400 may thencompare the quantity of GEM or GMC measured by the GCMS 404 to the knownquantity of GEM or GMC supplied by the permeation oven 460. In someembodiments, the gaseous mercury detection system 400 may use thecomparison to determine the accuracy of or calibrate the gaseous mercurydetection system 400. In other embodiments, the gaseous mercurydetection system 400 may be used to determine the known quantity of GEMor GMC supplied by the permeation oven 460.

The gaseous mercury detection system 400 may be fluidly coupled to asecond mercury detection system 482 that is used to further determinethe accuracy or calibrate the gaseous mercury detection system 400. Insome embodiments, the second detection system 482 may be incorporated inthe gaseous mercury detection system 400. For example, the seconddetection system 482 may be supported by the support structure 415. Inother embodiments, the second detection system 482 may be distinct fromthe gaseous mercury detection system 400. For example, the seconddetection system 482 may be remote from the gaseous mercury detectionsystem 400 and fluidly coupled to the gaseous mercury detection system400 via at least one sixth conduit 483.

In an embodiment, the first valve 454 may selectively direct GEM or GMCcollected to the second detection system 482. The GEM or GMC may becollected by the mercury collector 402 from ambient air or supplied bythe permeation oven 460. The first valve 454 may direct the GEM or GMCto the second detection system 482 in response to direction from thecontroller 446. The second detection system 482 may then measure aquantity GEM or GMC provided thereto.

The second detection system 482 may include any gaseous mercurydetection system. In an embodiment, the second detection system 482 maybe substantially similar to the gaseous mercury detection system 200shown in FIGS. 2A and 2B that has been previously calibrated. In theillustrated embodiment, the second detection system 482 may include anelemental mercury detector 484 (EMD). The EMD 484 may include any EMDknown in the art. For example, the EMD 484 may include a Tekran® 2537.In an embodiment, the EMD 484 may include a Tekran® 1130 coupled to aTekran® 1135 and a Tekran® 2537.

The second detection system 482 may further include a pyrolyzer 486positioned between the EMD 484 and the first valve 454 configured tocollect the GEM or GMC. In an embodiment, the pyrolyzer 486 may besimilar to the mercury collector 102 shown in FIG. 1. For example, thepyrolyzer 486 may include a pyrolyzer collection surface 490 configuredto collect GEM or GMC. The pyrolyzer collection surface 490 may includea potassium chloride collection surface. The pyrolyzer 486 and, inparticular, the pyrolyzer collection surface 490, may release the GEM orGMC when the pyrolyzer 486 is heated above the decomposition temperatureof at least one GMC that may be present. The second detection system 482may include a heater 488 configured to heat the pyrolyzer 486 above thedecomposition temperature of the at least one GMC.

In an embodiment, one or more components of the gaseous mercurydetection system 400 and the second detection system 482 may be heatedto a temperature between about 100° C. to about 300° C. (e.g., about150° C. to about 250° C., about 200° C.) when a mercury-containing gasflows therethrough. The one or more components of the gaseous mercurydetection system 400 and second detection system 482 may be heated tominimize (e.g., substantially prevent) the amount of GEM or GMC adheringto a surface of the one or more components. For example, the first valve454, the second valve 456, the fourth conduit 474, the fifth conduit480, the sixth conduit 483, the GCMS 404, or another component of thegaseous mercury detection system 400 may be heated to a temperaturebetween about 100° C. to about 300° C. (e.g., 150° C. to about 250° C.,about 200° C.) when the GEM or GMC flow therethrough. Additionally oralternatively, the one or more components of the gaseous mercurydetection system 400 and the second detection system 482 (e.g., thecontainers 672, the first valve 454, the fourth conduit 474, etc.) mayinclude a substantially nonpolar coating applied to an interior surfacethereof that contacts the GEM or GMC to minimize the amount of GEM orGMC that sticks thereto. The nonpolar coating may include, for example,deactivated fused silica, PDMS, or combinations thereof.

FIG. 5 is a flow diagram of a method 500 of using the gaseous mercurydetection system 400 shown in FIG. 4, according to an embodiment. Insome embodiments, some of the acts of the method 500 may be split into aplurality of acts, some of the acts may be combined into a single act,and some acts may be omitted. Also, additional acts may be added to themethod 500.

In act 505, the gaseous mercury detection system 400 measures a quantityof GEM or GMC that is present in ambient air. For example, the mercurycollector 402 may collect the GEM or GMC from ambient air that flowstherethrough. The mercury collector 402 and, in particular, thecollection surface 403 of the mercury collector 402, may release the GEMor GMC when the mercury collector 402 is heated to the first releasetemperature. The GEM or GMC may then be captured by the sample trap 410that is fluidly coupled to the mercury collector 402. The sample trap410 may release the GEM or GMC when heated to a second releasetemperature. The GEM or GMC exiting the sample trap 410 may exhibit ahigher concentration than the GEM or GMC exiting the mercury collector402. The GCMS 404 may measure the quantity of GEM or GMC presenttherein. In an embodiment, these steps may be in response to directionfrom the controller 446, or combinations thereof.

In act 510, the permeation oven 460 is heated to a selected temperatureconfigured to release a known quantity of GEM or GMC from one or morepermeation tubes 470 positioned therein. For example, the one or morepermeation tubes 470 may include at least one of elemental mercury or atleast one mercury compound therein. When the one or more permeationtubes 470 are heated to the selected temperature, the elemental mercuryor the mercury compound may form at least one of GEM or GMC. The GEM orthe GMC may be emitted from the permeation tubes 470 at a known emissionrate. In an embodiment, the emission rate of the permeation tubes 470 atthe selected temperature may be known prior to performing act 510 or maybe determined after act 510. In an embodiment, a gas that isnon-reactive with GEM or GMC emitted by the permeation tubes 470 mayflow through the permeation oven 460 to move the GEM or GMC towards theoven outlet 468. It should be noted that act 510 may be performed beforeor after act 505. The permeation oven 460 may be heated in response todirection from the controller 446.

In act 515, the GEM or GMC supplied by the permeation oven 460 aremeasured by the gaseous mercury detection system 400 to determine thequantity of GEM or GMC present. For example, the GEM or GMC may flowfrom the permeation oven 460 to the first valve 454 and from the firstvalve 454 to the second valve 456. In some embodiments, the second valve456 may direct the GEM or GMC to the sample trap 410. The sample trap410 may capture the GEM or GMC and then rapidly heat to release the GEMor GMC. The GEM or GMC exiting the sample trap 410 may exhibit a higherconcentration than the GEM or GMC exiting the permeation oven 460. Thesecond valve 456 may direct the GEM or GMC to the GCMS 404. The GCMS 404may measure the quantity of GEM or GMC supplied by the permeation oven460.

In act 520, the first valve 454 may direct some of the GEM or GMC to thesecond detection system 482. The GEM or GMC may first flow through thepyrolyzer 486 that collects the GEM or GMC and release GEM when heatedabove a decomposition temperature of at least one GMC present. The GEMmay then be analyzed by the EMD 484 to determine the quantity ofelemental mercury contained therein after the GMC is decomposed (e.g.,GEM and elemental mercury from the decomposed GMC). The GEM or GMC maybe directed towards the second detection system 482 and the seconddetection system 482 may measure the GEM or GMC in response to directionfrom the controller 446.

In act 525, the accuracy of the gaseous mercury detection system 400 isdetermined or the detection system is calibrated. For example, thequantity of the GEM or GMC collected by the mercury collector 402 fromambient air detected by the GCMS 404 may be compared to the quantity ofGEM or GMC collected by the mercury collector 402 from ambient airdetected by the second detection system 482. In an embodiment, the knownquantity of GEM or GMC supplied by the permeation oven 460 is comparedto the quantity of GEM or GMC supplied by the permeation oven 460 thatis measured by the GCMS 404. In an embodiment, the quantity of GEM orGMC supplied by the permeation oven 460 that is measured by the GCMS 404is compared to the quantity of GEM or GMC supplied by the permeationoven 460 that is measured by the second detection system 482.Alternatively, the gaseous mercury detection system 400 may use one ormore of the above comparisons to determine the accuracy of or calibratethe gaseous mercury detection system 400. For example, the gaseousmercury detection system 400 may use the comparison to determine acorrection factor that may compensate for any discrepancies between thetwo quantities.

The following working example provides further detail in connection withthe specific embodiments described above.

Working Example

A gaseous mercury detection system was provided that was similar to thegaseous mercury detection system 400 shown in FIG. 4. The gaseousmercury detection system detection system included a gas supply having ahigh purity helium source and a permeation oven fluidly coupled to thegas supply. The permeation oven included a container therein. Thecontainer included a one-quarter inch stainless steel tube that wascoated with SilcoNert® deactivated fused silica. A permeation tube wasplaced inside the container. The permeation tube included a one-eighthinch diameter polyfluoroalkoxy alkane heat-shrink tubing withpolytetrafluoroethylene plugs that sealed both ends of the permeationtube. Mercury bromide (HgBr₂) was placed within the permeation tubebetween the polytetrafluoroethylene plugs.

The gaseous mercury detection system also included a sample trap. Thesample trap was an SIS Model 961 cryogenic focusing unit. The sampletrap included a 0.25 millimeter inner-diameter deactivated fused silicatube. The gaseous mercury detection system included a first conduit thatfluidly coupled the permeation oven to the sample trap. The firstconduit included stainless steel tubing that had an inner surfacethereof coated with SilcoNert® deactivated fused silica. The firstconduit also included two stainless steel VICI GC valves that had aninner surface coated with SilcoNert® deactivated fused silica.

The gaseous mercury detection system also included a Shimadzu QP2010Ultra GCMS. The GCMS included a column and a mass spectrometer. Thecolumn included a 30-meter long tubing that had a 0.25 mm innerdiameter. The inner surface of the tubing was coated with PDMS. The massspectrometer included an electron ionizer. Finally, the gaseous mercurydetection system included a second conduit that fluidly coupled thesample trap to the GCMS. The second conduit included stainless steeltubing that had an inner surface thereof coated with SilcoNert®deactivated fused silica.

During operation, the permeation tube was heated to about 100° C. toform a mercury-containing gas. A 30 millimeter per minute flow of highpurity helium gas was flowed through the container to transport themercury-containing gas emitted from the permeation tube to the sampletrap. The mercury-containing gas flowed from the permeation oven to thesample trap via the first conduit which was heated to about 220° C. Thetrapping surface of the sample trap was cooled to about 0° C. to capturethe mercury-containing gas. The trapping surface was allowed to capturethe mercury-containing gas for about 5 minutes after which the trappingsurface was rapidly heated to about 220° C. The trapping surface washeld at about 220° C. for about 10 minutes (e.g., the time it took theGCMS to measure the at least one mercury-containing gas). Themercury-containing gas flowed from the sample trap to the GCMS via thesecond conduit, which was heated to about 200° C. The quantity of themercury-containing gas was then measured by the GCMS.

FIGS. 6A and 6B are graphs outputted by the GCMS after the GCMS measuredthe quantity of the mercury-containing gas. FIG. 6A is a chromatogram605 that plots relative intensity (e.g., abundance) of themercury-containing gas measured by the GCMS as a function of time. Thechromatogram 605 includes first peak 610 at about 2.8 minutescorresponding to GEM and a second peak 615 at about 3.4 minutescorresponding to mercury bromide. The chromatogram 605 illustrates thatthe gaseous mercury detection system can measure both GEM and GMC. FIG.6B is a mass spectrum 620 of the mercury-containing gas detected by theGCMS at about 3.4 minutes. The mass spectrum 620 plots the relativeintensity of the gas detected at about 3.4 minutes as a function of itsmass to charge ratio (m/z). The mass spectrum 620 includes a first peak625 that corresponds to GEM (²⁰²Hg),) a second peak 630 that correspondsto HgBr (²⁰²Hg+⁷⁹Br), and a third peak 635 that corresponds to HgBr₂(²⁰²Hg+⁷⁹Br+⁸¹Br). At least some of the GEM shown in the chromatogram605 may be caused by decomposition of the mercury bromide caused by theelectron ionizer. Using the information shown in FIGS. 6A and 6B, thedetection system may determine the quantity of GEM and GMC present inthe mercury-containing gas.

FIG. 7 is a schematic diagram of a calibration system 700, according toan embodiment. The calibration system 700 may be used to calibrate anygaseous mercury detection system disclosed herein or any conventionalgaseous mercury detection system. The calibration system 700 isconfigured to supply a known quantity of mercury-containing gas to agaseous mercury detector 792. The gaseous mercury detector 792 maydetect a quantity of GEM or GMC. The calibration system 700 may alsoinclude a controller 746 that is communicably coupled to the calibrationsystem 700 and the gaseous mercury detector 792. The controller 746 maybe configured to compare the quantity of the GEM or GMC detected by thegaseous mercury detector 792 to the known quantity of the GEM or GMCprovided by the calibration system 700. As such, the controller 746 mayat least one of determine an accuracy of or calibrate the gaseousmercury detector 792.

The calibration system 700 may include a support structure 715.

The calibration system 700 further includes a permeation oven 760. Thepermeation oven 760 may be substantially similar to the permeation oven460 shown in FIG. 4. For example, the permeation oven 760 may includeone or more permeation tubes 770 positioned therein. The permeation oven760 may also include a filament or other heating device (not shown)configured to heat the one or more permeation tubes 770 to a selectedtemperature. The one or more permeation tubes 770 may include elementalmercury or a mercury compound therein. The elemental mercury or themercury compound partially vaporizes or otherwise forms GEM or GMC(e.g., at least one mercury-containing gas). The one or more permeationtubes 770 emit the mercury-containing gas at a known (e.g., alreadyknown or determinable) emission rate at the selected temperature. Assuch, the permeation tubes 770 may supply a known quantity of themercury-containing gas.

In an embodiment, the permeation oven 760 may be fluidly coupled to agas supply 772 that supplies the permeation oven 760 with a supply of agas that is non-reactive with the mercury-containing gas (e.g., Argon,Helium, or another noble gas and/or another inert gas). The gas maytransport the mercury-containing gas from the permeation oven 760. Insome embodiments, the permeation oven 760 may be configured to flow aselected amount of the gas around each permeation tube 770. For example,at least one permeation tube 770 may be placed in container 776 that isconnected to an orifice 778. The orifice 778 may be configured to onlyallow a selected amount, rate, or pressure of the gas to flow throughthe container 776.

The calibration system 700 may further include one or more valvesconfigured to direct the mercury-containing gas that exits thepermeation oven 760 to other components of the calibration system 700.For example, the one or more valves may include a first valve 754 and asecond valve 756. The first valve 754 may fluidly couple the permeationoven 760 (e.g., fluidly coupled to each container 776) to the secondvalve 756. The second valve 756 may be configured to direct the at leastone mercury-containing gas to one or more different components of thecalibration system 700. For example, the second valve 756 may be fluidlycoupled to a pyrolyzer 786. In an embodiment, the second valve 756 maydirect the mercury-containing gas to a mercury collector (not shown) orsample trap (not shown). The pyrolyzer 786, the mercury collector, orthe sample trap may release the mercury-containing gas when heated abovetheir respective release temperatures. The calibration system 700 mayinclude a conduit 794 that fluidly couples the pyrolyzer 786, themercury collector, or the sample trap to the gaseous mercury detector792. In another example, the second valve 756 may also be fluidlycoupled to the conduit 794.

In an embodiment, the first valve 754, the second valve 756, conduit794, or another component of the calibration system 700 may be heated toa temperature between about 100° C. to about 300° C., such as about 150°C. to about 250° C. or about 220° C. to minimize (e.g., substantiallyprevent) the at least one mercury-containing gas from sticking to thesurfaces thereof. Additionally or alternatively, the first valve 754,the second valve 756, conduit 794, or another component of thecalibration system 700 that comes in contact with the mercury-containinggas may be coated with a substantially nonpolar coating, such as adeactivated fused silica coating (e.g., SilcoNert® deactivated fusedsilica) and/or a PDMS coating. The coating may help minimize (e.g.,substantially prevent) the mercury-containing gas from adhering to thecomponents of the calibration system 700.

The conduit 794 fluidly couples the calibration system 700 to thegaseous mercury detector 792. The gaseous mercury detector 792 mayreceive the known quantity of the mercury-containing gas and detect thequantity of the mercury-containing gas. The gaseous mercury detector 792may be substantially similar to the gaseous mercury detection system 200shown in FIGS. 2A and 2B or the second detection system 482 shown inFIG. 4.

The controller 746 may be communicably coupled to one or more componentsof the calibration system 700 and the gaseous mercury detector 792. Inan embodiment, the controller 746 may control the one or more componentsof the calibration system 700 and the gaseous mercury detector 792. Inan embodiment, the controller 746 may compare the quantity of the atleast one mercury-containing gas detected by the gaseous mercurydetector 792 with the known quantity of the at least onemercury-containing gas supplied by the calibration system 700. Thecontroller 746 may use this comparison to determine the accuracy of thegaseous mercury detector 792 and calibrate the gaseous mercury detector792 using any of the calibration techniques previously discussed.

Embodiments of the present disclosure may be embodied in other specificforms without departing from its spirit or essential characteristics.The described embodiments are to be considered in all respects only asillustrative, and not restrictive. All changes which come within themeaning and range of equivalency of the foregoing description are to beembraced within the scope of the invention.

What is claimed is:
 1. A gaseous mercury detection system, comprising: amercury collector, including a mercury collection surface, the mercurycollector configured to: cool the mercury collection surface to atemperature of about 5° C. above an ambient water dew point temperature;and collect on the mercury collection surface at least one of gaseouselemental mercury (GEM) or a gaseous mercury compound (GMC) from amercury-containing gas; a heater positioned and configured to heat themercury collection surface to a first release temperature and releasethereby the at least one of GEM or GMC collected, wherein the firstrelease temperature is below a decomposition temperature of the at leastone GMC; a sample trap fluidly coupled to the mercury collector, thesample trap configured to: capture the at least one of GEM or GMCreleased from the mercury collector at a temperature of about 0° C. orless, and release the at least one of GEM or GMC captured in the sampletrap at a second release temperature, the second release temperaturebeing below the decomposition temperature of the at least one GMC; and agas-chromatography mass spectrometer fluidly coupled to the sample trapto receive the at least one of GEM or GMC released from the sample trap.2. The gaseous mercury detection system of claim 1, wherein the firstrelease temperature is between about 100° C. to about 300° C.
 3. Thegaseous mercury detection system of claim 1, further comprising acalibration system, the calibration system including: a permeation ovenconfigured to be heated to a selected temperature, the permeation ovenfluidly coupled to the gas-chromatography mass spectrometer; and one ormore permeation tubes positioned within the permeation oven, each of theone or more permeation tubes including at least one of elemental mercuryor a mercury compound and configured to release the at least one of theelemental mercury or the mercury compound stored therein at the selectedtemperature as GEM or GMC.
 4. The gaseous mercury detection system ofclaim 3 wherein the permeation oven is fluidly coupled to thegas-chromatography mass spectrometer through the sample trap.
 5. Thegaseous mercury detection system of claim 3, further comprising: a GEMdetector fluidly coupled to the permeation oven and configured to detectthe GEM; a valve fluidly coupled to the permeation oven, the valveconfigured to selectively control flow of the at least one of GEM or GMCreleased by the one or more permeation tubes to the gas-chromatographymass spectrometer or the GEM detector; and a pyrolyzer disposed betweenthe GEM detector and the valve, the pyrolyzer configured to heat the atleast one GMC to form GEM.
 6. The gaseous mercury detection system ofclaim 5, further comprising one or more conduits that fluidly couple thepermeation oven with the gas-chromatography mass spectrometer, the oneor more conduits heated to a temperature of about 100° C. to about 300°C. during operation.
 7. A method of collecting and releasing gaseouselemental mercury (GEM) or a gaseous mercury compound (GMC) in ambientair, the method comprising: cooling a collection surface to a collectiontemperature of about an ambient water dew point temperature; drawingover the collection surface the ambient air at a collection flow rate;collecting on the collection surface substantially all of the at leastone of GEM or GMC present in the ambient air; heating the collectionsurface to a temperature sufficient to release the at least one of GEMor GMC therefrom and below a decomposition temperature of the at leastone GMC; and releasing from the collection surface substantially all ofthe at least one of GEM or GMC collected thereon.
 8. A method ofmeasuring a quantity of gaseous elemental mercury (GEM) or a gaseousmercury compound (GMC) in ambient air, the method comprising: cooling acollection surface to a collection temperature of about an ambient waterdew point temperature; drawing over the collection surface the ambientair at a collection flow rate; collecting on the collection surfacesubstantially all of the at least one of GEM or GMC present in theambient air; heating the collection surface to a temperature sufficientto release the at least one of GEM or GMC therefrom and below adecomposition temperature of the at least one GMC; releasing from thecollection surface substantially all of the at least one of GEM or GMCcollected thereon; cooling a sample trap to a temperature of about 0° C.or less; capturing the at least one of the GEM or GMC released from themercury collector with a sample trap; heating the sample trap to atemperature greater than about 100° C. and below the decompositiontemperature of the at least one GMC; desorbing the at least one of GEMor GMC from the sample trap; and after heating the sample trap,measuring at least one of a quantity of the GEM or GMC using agas-chromatography mass spectrometer.
 9. The method of claim 8, whereinheating the collection surface includes heating the collection surfaceto a temperature of about 100° C. to about 300° C.
 10. The method ofclaim 8, wherein cooling the collection surface to a collectiontemperature includes cooling the collection surface to a collectiontemperature of five degrees above the ambient water dew pointtemperature.
 11. The method of claim 8, wherein the collection flow rateis about 10 to about 100 liters per minute.
 12. The method of claim 8,wherein the cooling the sample trap includes cooling the sample trap toa temperature of about −50° C.
 13. The method of claim 8, wherein thecollecting on the collection surface occurs over a period of 30 minutesto two hours.
 14. The method of claim 8, further comprising, prior tomeasuring, ionizing the at least one mercury-containing gas using anelectron ionizer.
 15. The method of claim 8, further comprising, priorto measuring, ionizing the at least one mercury-containing gas using achemical ionizer.
 16. The method of claim 8, further comprisingcalibrating the gas-chromatography mass spectrometer, whereincalibrating the gas-chromatography mass spectrometer includes: heating apermeation oven to a selected temperature, the permeation oven includingone or more permeation tubes therein having at least one of elementalmercury or a mercury compound and configured to release the at least oneof the elemental mercury or the mercury compound stored therein at theselected temperature as GEM or GMC; and measuring the quantity of the atleast one of the GEM or the GMC released by the one or more permeationtubes using the gas-chromatography mass spectrometer.
 17. A calibrationsystem, comprising: a permeation oven configured to be heated to aselected temperature; one or more permeation tubes positioned within thepermeation oven, each of the one or more permeation tubes includingelemental mercury or a mercury compound and configured to release theelemental mercury or the mercury compound stored therein at the selectedtemperature as gaseous elemental mercury (GEM) or a gaseous mercurycompound (GMC); a GEM detector configured to detect the GEM; and one ormore conduits coated with a substantially nonpolar coating andconfigured to fluidly couple the permeation oven to the GEM detector,the one or more conduits further configured to be heated to atemperature above about 120° C. during operation.
 18. The calibrationsystem of claim 26, further comprising a pyrolyzer configured to heatthe at least one of GEM or at least one GMC to a temperature above thedecomposition temperature of the GMC.